Melt the chocolate in a water bath. Next to the fire, add the butter and beat with a whisk until the mixture has a creamy consistency.
Stir in the egg yolks and allow to cool a little, this mixture must be just lukewarm – otherwise it would be too liquid to be mixed intimately with the egg whites.
Whip the egg whites to stiff peaks – after about 2 minutes add the sugar to make this easier. The chocolate mixture on this foam form and gently fold.
You can serve the chocolate foam in portion pots (ramequins) or in a large bowl. In this case, use a potato peeler to cut narrow shavings from a chocolate bar and decorate the mousse with them, then dust with powdered sugar. Or you can decorate the main mass with a part of the mousse sprinkled over it from a piping bag with a serrated nozzle. In any case, a chocolate mousse must be served well chilled. Serve with brioche slices or dry petits fours.
Translator’s note: The recipe is characterized by high quality – but the mousse is just as extraordinarily rich. It is lightened by using whipped cream instead of butter and by adding a tiny bit more egg white.
Tip: Feel free to use better chocolate – the more delicious the result!